a) Field of the Invention
The present invention relates to a novel thermoplastic resin composition which can be utilized as a material for producing molded articles by injection molding, extrusion molding or a like means.
b) Related Art
Generally, polyphenylene ethers are excellent in heat resistance, hot water resistance, dimension stability, and mechanical and electrical properties. On the other hand, they have disadvantages; for example, they show unsatisfactory moldability due to their high melt viscosity, poor chemical resistance, and low impact resistance.
Known methods for improving moldability by lowering the melt viscosity of polyphenylene ethers while maintaining their excellent properties include use of a mixture of a polyphenylene ether and a polystyrene resin. However, these known methods still fail to improve chemical resistance.
On the other hand, propylene polymers are not only excellent in various properties such as moldability, toughness, water resistance, chemical resistance, etc., but also they have low specific gravity and are cheap in cost; they have been widely used as a material for preparing various molded articles, films, sheets, etc.
However, the propylene polymers have defects or points which need to be improved in heat resistance, rigidity, impact resistance, coatability, adhesiveness, etc., which creates an obstacle in developing new practical utility. In particular, improvement in the heat resistance and impact resistance thereof is strongly desired.
Naturally, it may be expected to blend a polyphenylene ether and a propylene polymer to prepare a resin composition which could have the advantages of the both polymers and which could have improved moldability and impact resistance, and thus a wide possibility of new application would be available.
Blending a polyphenylene with a propylene polymer, however, actually gives rise to a resin composition in which compatibility of both polymers is poor so that molded articles obtained from such a blend as by injection molding, suffers phase separation between the polyphenylene ether and the propylene polymer, thereby providing articles having an extremely poor appearance and poor mechanical properties, which are unsatisfactory for practical purposes. However, there has been a strong demand for a composition of polyphenylene ether having high impact resistance and good weatherability while maintaining its inherent heat resistance.
A method for improving the compatibility between a polyphenylene ether and a propylene polymer is known, as described in Unexamined Japanese Pantent Publication No. 207349/1989, in which method a polyphenylene ether is blended with a propylene polymer modified with a styrene based monomer by graft copolymerization.
On the other hand, it is known as a method for improving impact strength that a rubbery substance is blended with and is dispersed in a polyphenylene ether.
The rubbery substance has to be dispersed uniformly in the polyphenylene ether resin so as to obtain a composition having high impact strength.
However, where the rubbery substance is blended with a composition comprising a polyphenylene ether and a modified propylene polymer grafted with a styrene-based monomer, or blended with a composition comprising a polyphenylene ether and a composition containing the modified propylene polymer and a propylene polymer, large portion of the rubbery substance is inclined to disperse in the polyphenylene ether or in the modified propylene polymer, and thus this method fails to provide a composition having high impact resistance.
In view of the above points, the present inventors have studied intensively and extensively in order to develop effective technology which lends itself to the improvement of a resin composition composed of a polyphenylene ether, propylene polymer and rubbery substance.
As the result, they have found that a new resin composition having its impact resistance greatly improved is obtained by using as its rubbery substance, two or more rubbery substances, with at least one of the substances being compatible with a polyphenylene ether or a composition containing the polyphenylene ether, and with at least one of the substances being not compatible with a polyphenylene ether or a composition containing the polyphenylene ether. This finding led to the present invention.